An air-swept mill as a crushing or comminuting device is known from DE-AS 1152297. In this air-swept mill an annular space with a blade ring is bounded by a casing wall with a reinforcing cladding as a protection against wear and a grinding surface or track with a weir. The outlet cross-section of the flow channels or ducts and the radial width of the annular space are constant and predetermined by the fixed, annular reinforcing cladding and the stationary weir. A hydraulic influencing of the feed flow is to be made possible by interchangeable blades with a clearly defined surface curvature.
Another known air-swept mill in the form of a flexible roller mill is known from German patent 189,039 and has an annular space, a weir on the grinding ring and a reinforcing cladding-like baffle wall. In order to concentrate the grinding material and fluid on the gaps between the grinding rollers, guide blades are fixed close to the centre of the grinding pan and to the casing wall. A cover ring and the baffle wall on the casing wall cover an annular space up to opening areas, which are radially adjacent to the grinding rollers. The grinding material fluid flow is deflected into the interior of the grinding chamber and below the grinding rollers. As a result of the high flow rate and the deflections turbulence occurs in the overall flow, which in the same way as inhomogeneities of the grinding bed has a disadvantageous influence on the energy balance and the effectiveness of the method and apparatus.
DE 31 34 601 C2 described an air-swept mill, in which the fluid flow is guided with the aid of feed elements to the points at which the ground material occurs. The feed elements have horizontal legs of varying length and are in each case positioned between two blades of the blade ring.
DE-OS 23 09 900 discloses an air-swept mill, whose reinforcing cladding comprises segments which can be placed on one another. Each segment is detachably fixed with two screw elements and has two upper and lower, in each case differently inclined trapezoidal surfaces as wearing surfaces. By a 180.degree. turn about the longitudinal axis or the vertical axis an unworn surface and edge can be exposed to the feed flow. Turning about the longitudinal axis simultaneously brings about a modified, e.g. sharper deflection of the feed flow and the grinding material particles hurled into the annular space. However, the turning is time-consuming and leads to down-times, giving rise to an increase in operating costs. If only individual reinforcing cladding segments are turned for a local sharper deflection of the feed flow and are in this way adjusted, turbulence of the fluid particle flows can lead to pressure fluctuations in the grinding--classifying chamber and to inhomogeneities in the vicinity of the grinding bed, which impair the grinding capacity.
The known methods and apparatuses provide for an influencing of the grinding process with the aid of a fluid flow, which is deflected with a corresponding speed in a predetermined direction, particularly in the direction of or between the grinding rollers. For deflection purposes use is made of static means, which can only be modified after interrupting the grinding process and by dismantling or reconstruction.
The complex processes in the air-swept mill, the fact that the different parameters are dependent on one another, the influence on the grinding bed and the particle size distribution are only inadequately taken into account, so that the grinding capacity, energy consumption, fine-grain fraction, etc., cannot achieve optimum values.